Terminals for mobile communication devices such as portable telephones or the like are progressing in downsizing. Most mobile communication devices are equipped with a built-in antenna inside housing recently. FIG. 7A shows a perspective view of a conventional mobile communication device, and FIG. 7B shows a perspective side view of the same.
Circuit board 101 is disposed in housing 100. Display 109, input unit 111, circuit 110 and planar inverted-F antenna (hereafter referred to “antenna”) 108 are disposed in housing 100, and are connected to circuit board 101 respectively.
FIG. 8 shows an exploded perspective view of conventional antenna 108. Ground plate 102 is provided on circuit board 101. Radiator 103 is disposed facing circuit board 101. Short line 104 connects radiator 103 with ground plate 102. Feed line 105 is connected to radiator 103. Feed terminal 106 connects feed line 105 with a circuit (not shown). Slit 107 is formed in radiator 103.
By adjusting a gap distance between short line 104 and feed line 105, the impedance of antenna 108 is varied to implement an impedance matching. A length of slit 107 is varied to adjust the gap distance between short line 104 and feed line 105. Japanese Patent Application Unexamined Publication No. H4-157908 discloses an example of such antenna.
To implement the impedance matching by adjusting the length of slit 107, however, slit 107 must be extended causing radiator 103 to have a larger area. This would result in a larger shape of antenna 108, and eventually cause a difficulty in the device downsizing. Moreover, extending slit 107 requires changing the geometry of antenna 108 itself that needs redesigning of molds to produce antenna 108, thus it is not an easy task.